Self-igniting internal combustion engines, sometimes referred to as Diesel engines, must be supplied under all operational conditions with the exact amount of fuel necessary for combustion so as to prevent excessive magnitudes of any of the exhaust gas components HC, CO, NO.sub.X or excessive smoke. Under all circumstances, even when exhaust gas recycling is used in order to reduce the amount of NO.sub.X, the fuel quantity which is injected should never exceed the quantity for which sufficient combustion air is available. Further conditions which must be met by the fuel supply system are a constant idling speed, favorable drivability and automatic starting control. Still further objectives are the suppression of any bucking of the vehicle and of the engine and a certain amount of insensitivity against aging and increasing mechanical tolerances in the system.
A Diesel engine requires a precisely determined minimum amount of air for each and every operational condition, i.e., a given engine speed (rpm), load, temperature, etc., in order that the limits of exhaust gas constituents are not exceeded. The associated multi-dimensional characteristic data sets cannot be embodied in mechanical devices. In contemporary Diesel engines, it is customary to provide a given amount of fuel with the expectation that the engine will be able to aspirate sufficient air to completely combust the fuel. However, in modern designs of engines which must meet constantly increasing demands with respect to power while maintaining a relatively small size the adequate supply of oxygen into the combustion chambers may not be guaranteed at all times.